This application claims priority to applications entitled xe2x80x9cApparatus and Method of Controlling Forward Link Power When in Discontinuous Transmission Mode in a Mobile Communication Systemxe2x80x9d filed in the Korean Industrial Property Office (KIPO) on Jul. 8, 1999 and assigned Ser. No. 99-27390, and xe2x80x9cApparatus and Method for Detecting Frame of Discontinuous Transmission Mode Mobile Communication Systemxe2x80x9d filed in the KIPO on Jun. 28, 1999 and assigned Ser. No. 99-25052, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an apparatus and method of controlling a power in a mobile communication system, and more particularly to an apparatus and method of controlling forward link power while in discontinuous transmission mode.
2. Description of the Related Art
Typically, discontinuous transmission mode (DTX) is a mode that transmits data in a frame unit only when there is data to be transmitted in a wired system or a mobile communication system. Discontinuous transmission mode is used for the following advantages. Since data frames are transmitted only when data actually exists, transmission power can be minimized, and the strength of the interference signal affecting the system is reduced, so that the capacity of the whole system is increased.
However, since the transmitter discontinuously transmits frames, the receiver cannot recognize whether a frame is transmitted, and this causes a base station not to be able to perform forward link power control by itself. Specifically, when the receiver of a terminal cannot accurately judge whether a frame is transmitted, the receiver of the terminal cannot trust judgment variables of a decoder including a cyclic redundancy code (CRC) and so on, and the result of decoding decision of its decoder. Since the result of judgment cannot be trusted, the existing method used in continuous transmission mode cannot accurately control the transmission power of the base station when in discontinuous transmission mode. Hereinafter, an example of the conventional forward link power control method performed in the receiver of the discontinuous transmission mode mobile radio communication system will be explained.
FIG. 1 is a block diagram of the conventional forward link power control apparatus of the receiver and the transmitter in the discontinuous transmission mode mobile communication system. Here, it is assumed that the mobile communication system is a code division multiple access (CDMA) communication system.
Referring to FIG. 1, a radio frequency (RF) section 10 converts an RF signal received through an antenna ANT into a baseband frequency by frequency-down-converting the RF signal. A receiver 12 despreads the output signal of the RF section 10, and determines the level of a symbol by accumulating the despread signals in a symbol unit. At this time, the despreading includes PN despreading and orthogonal despreading. A decoder 14 of the receiver checks whether the received frame is in a good state or in an erasure state by checking the received frame thereby checking the condition of the channel. A control section 16 transmits the result of checking from the decoder 14 backward to the base station. When the result of channel checking, which is transmitted backward to a power control section (not illustrated in FIG. 1) of the base station, is in a good state, the power control section judges that the channel is in a good state, and reduces the forward transmission power. On the other hand, when the result of channel checking is in an erasure state, the judgment of the power control section depends on whether the base station had transmitted a prior frame. If the base station had transmitted a prior frame, the power control section judges that the channel is in an erasure state, and increases the forward transmission power, while if the base station has not transmitted a prior frame, the power control section ignores the result and thus does not reflect the command in the forward link power control.
Accordingly, when in discontinuous transmission mode, the conventional forward link power control method has the drawback that the forward link power control command that is transmitted backward is used only when the transmitted data frame exists, the speed at which the forward link power control is adjusted becomes greatly lowered. In other words, when in discontinuous transmission mode where the amount of transmitted data is very small, power control is performed at a very low speed that is much less than the power control speed of 50 Hz in continuous transmission mode, and thus the forward link power control cannot follow the speed of the channel change. As a result, an apparatus and method of more rapidly and accurately controlling the forward link power when in discontinuous transmission mode are needed.
An object of the present invention is to provide an apparatus and method of controlling link power based on an accurate judgment of channel state by a terminal in a mobile communication system when in discontinuous transmission mode.
It is another object of the present invention to provide an apparatus and method of controlling a link power using channel state information received from a terminal in a mobile communication system when in discontinuous transmission mode.
In order to achieve the above and other objects, according to one aspect of the present invention, there is provided an apparatus for discriminating the existence or nonexistence of discontinuous transmission mode data while in discontinuous transmission mode. The apparatus comprises a location detector for detecting the location of energy of power control bits and the location of energy of non-power control bits in received data, a first energy measuring device for measuring the energy of a signal corresponding to the location of the non-power control bits outputted from the location detector, a second energy measuring device for measuring the energy of a signal corresponding to the location of the power control bits outputted from the location detector, and a control section for discriminating the existence or nonexistence of data by calculating an output ratio of the first energy measuring device to the second energy measuring device.
The data existence or nonexistence discriminating apparatus according to the present invention further comprises a decoder for detecting a CRC state in case that the transmitted data includes a CRC, wherein the control section discriminates the existence or nonexistence of the data along with the CRC state value.
The control section comprises an energy ratio calculator for calculating a ratio of the energy value of the first energy measuring device to the energy value of the second energy measuring device, a first comparator for comparing the output of the energy ratio calculator with a predetermined threshold value according to the existence/nonexistence of the data, and a controller for detecting the existence or nonexistence of data according to the output of the first comparator.
The data existence/nonexistence discriminating apparatus according to the present invention further comprises a second comparator for comparing the accumulated energy value of the power control bits with a minimum threshold value when data exists, wherein the control section discriminates the existence or nonexistence of data using the above outputs and an output of the second comparator.
The data existence/nonexistence discriminating apparatus according to the present invention further comprises a transmitter for transmitting the signals as described above to a base station in the mobile communication system.
The transmitter comprises a channel information inserter for transmitting the detected data state information as a power control command, a multiplexer for multiplexing the data outputted from the channel information inserter and reverse pilot channels, and a reverse transmitter for converting and transmitting an output of the multiplexer as a transmission signal.
The transmitted power control command may be composed of one-bit information representing xe2x80x98sufficientxe2x80x99 and xe2x80x98insufficientxe2x80x99, or may be composed of two-bit information representing xe2x80x98goodxe2x80x99, xe2x80x98uncertainxe2x80x99, xe2x80x98passxe2x80x99, and xe2x80x98badxe2x80x99.
In another aspect of the present invention, there is provided an apparatus for controlling forward link power according to a power control command included in received discontinuous transmission mode data while in discontinuous transmission mode. The apparatus comprises a power control command demodulator for extracting the power control command from the received data in order to provide the power control command, a controller for combining demodulated information and information representing whether a previous frame has been transmitted, and for generating and outputting power control bits for reducing the power only when the two information coincide, and a forward transmitter for transmitting the data and the power control bits under the control of the controller.
In still another aspect of the present invention, there is provided a method of generating a power control command based on a received frame that includes a plurality of slots, each of which includes power control bits. The method comprises the steps of providing the ratio of the power control bits to noise, which is given by the ratio of the energy accumulated value of the power control bits in the slots to the energy accumulated value of noise in the slots, and generating the power control command based on a ratio of the energy accumulated value of traffic symbol bits in the slots to the energy accumulated value of the power control bits when the provided ratio of noise power control bits is good.
A power control command generating method according to the present invention further comprises the steps of detecting CRC information if the frame includes CRC information, checking a decoded state of the detected CRC information, and generating a power control command for reducing power if decoding of the CRC information has been accurately performed.
A power control command generating method according to the present invention further comprises the step of generating a power control command for increasing power if decoding of the detected CRC information has not been accurately performed.